
#include<stdio.h>

  int main()
{
    int n,i=1,sign=-1;

    double deno=1,sum=0,term;

    scanf("%d",&n);

    while (i<=n)
{

    sign=-(1)*sign;
    term=sign*(1.0)/deno;
    sum=sum+term;
    deno=deno+2;
    i=i+1;
}
    printf("%.6f\n",sum);

    return 0;

}
